ABSTRACT

The Townsend Ground Squirrel Spermophilius townsendi is a small gray squirrel found in Nevada and western Utah. This squirrel is considered a pest due to the damage it causes to alfalfa and other agronomic crops. The reduction in crop yields and the cost of controlling the squirrels is costing farmers in western Utah over $100,000 annually. Current control programs such as shooting, flooding, treating with gopher bait and using fumigants have not been effective. For the past two years a program to educate land owners and introduce a new baiting program has been offered by the Utah State University Extension. The program consists of applying a pre-bait of oats several day prior to applying zinc phosphide (bait) in the spring, before the alfalfa greens up. To determine the effectiveness of the pre-baiting program we set up trials in 2009 and 2010. We selected 12 plots in 4 different fields. In each field there were 3 treatments: pre-baiting with oats and then applying the bait, applying only the bait and a control plot where there was no application of pre-bait or bait. Each plot was observed each day for 3 days before treatment and 3 days after treatment. Results of the two year trial showed that the plots that were pre-baited and then baited showed 71% control compared to 55% control on the bait only plots and 33% control on untreated plots. The farmers that have implemented this control program are reporting a reduction of ground squirrels in their fields.

Introduction

Townsend’s ground squirrels’ Spermophilius townsendi populations on agricultural lands in Beaver County, Utah are increasing. High populations of ground squirrels can compete with livestock for forage; destroy food crops, golf courses, and lawns; and can be reservoirs for diseases such as plague. Burrow mounds not only cover and kill vegetation, but damage haying machinery. The impact of high squirrels densities in irrigated alfalfa fields may have been exacerbated because of recent drought conditions and changing irrigation methods. While we are concerned with populations in one county in Utah, the effects can be reported throughout croplands where this species exists.

Ground squirrels in Beaver County are not a protected species. Townsend ground squirrels live in colonies and construct underground burrows that have a number of entrances. They hibernate during the coldest part of the winter. Males usually become active above ground 1 to 2 weeks before the females in the spring, sometimes as early as late February or early March. A few may be active above ground throughout the year. Breeding occurs immediately after hibernation. The young are born after a 4-to 5-week gestation period with 2 to 10 young per litter. Generally only 1 litter is produced each year. Densities of the ground squirrel populations can range from 2 to 20 or more per acre. At this density it is difficult for a farmer to obtain a profit from the harvest, due to the amount of damage incurred to the property and crop.

This assessment, suggested that for farmers to better mitigate the damage associated with overabundant squirrel populations, an integrated management effort must be initiated involving affected cooperators. At the time of the assessment some cooperators were implementing some controls, but the effort was not uniformly being applied by most farmers. To be effective, farmers adjacent to each other should be cooperating to systematically apply a control method. Therefore, Beaver County Extension developed and implemented a strategy, described below, to allow local farmers to improve their squirrel management techniques.

Compare the effectiveness of baiting and pre-baiting in field trials using rodenticides registered in Utah to control ground squirrels.

Methods

To train and inform our constituents, we held a workshop in January 2009 and 2010 in Beaver County to educate producers on the biology and methods that could be used to mitigate damage caused by Townsend ground squirrels. Each participant took a pre-test containing 20 questions about ground squirrel biology and damage control methods. After the test, we presented information regarding ground squirrel biology, ecology, damage, and management. Many of the workshop participants had experience with using several different control methods and they were able to participate in an active discussion of the advantages and limitations of each method. For example, many of the farmers were shooting the squirrels or were using commercial gopher poison (pellet bait) to try to control the squirrels, but the squirrels wouldn’t eat the pellet bait. Additionally, most producers were waiting till the alfalfa fields greened up in the late spring to start baiting; this was ineffective because the ground squirrels preferred to eat alfalfa rather than the bait.

Workshop participants were shown how to prebait their fields with a crimped oat and then follow up several days later with grain containing zinc phosphide (bait). This control program had several possible advantages over other treatments producers were currently using, such as: 1) squirrels are much more likely to eat and develop a taste for the grain bait if they were provided a untreated grain pre-bait shortly after they emerge from hibernation and prior to vegetation green-up, 2) both prebait and bait can be applied quickly using a spreader on a four wheeler compared to other methods where you have to treat each individual hole, and 3) by applying the bait when adults emerge from hibernation, you can target the breeding population thus preventing reproduction.

To measure the informational component of the workshop a post-test was administered at the end of the workshop that included the questions in the pre-test.

In addition to the workshop, we created a trial field site to demonstrate to producers the effectiveness of the pre-baiting. To establish these trials, we worked with four different cooperators to set up plots within their fields. We selected 12 plots, in 4 cooperators’ fields, 1 of each of 3 treatment types. Each plot was 50 X 50 m and at least 400 meters from each other. The 3 treatments were as follows: 1) Plot 1 was pre-baited with crimped oats and then baited with zinc phosphide; 2) Plot 2 was baited with zinc phosphide without pre-baiting, and 3) Plot 3 received no treatments. Within each field, the plots were randomly assigned to a treatment. Each plot was observed for 3 days before treatment and 3 days after treatment to determine if the number of squirrels decreased. The plots were prebaited with crimped oats using a hand spreader. The bait was spread using the same spreader. The fields used in the study differed each year.

Results

The pre-test was completed by 35 workshop participants. The average score was 63% (range 45-90%). The post-test was completed by 32 workshop participants. The average score was 84% (range 65-100%).

In 2009, the plots that were treated with bait only showed an average reduction of squirrels from 8.3 to 3.4 which represent 59% control. In 2010 the bait only plots showed a continued reduction going from 6.3 squirrels to 3.3 which represents 52%.

The 2009 plots that were prebaited and then baited showed an average reduction of squirrels from 10.7 to 2.7 which represent 75% control. The 2010 plots which were prebaited and then baited showed an average reduction of squirrels from 6.9 to 2.3 which represent 66% control.

The control plots with no treatment still showed a reduction of ground squirrels from 5.4 to 3.6 which represent 32.5% control in 2009 and 6.3 to 4.3 which represent 32.5% in 2010. This reduction in the number of squirrels in the control plots may be from farmers baiting and shooting the squirrels in the fields near the plots during the trial period (Table 1.).

Table 1. The number of observed Townsend ground squirrels before and after each treatment per plot.

Before Treatment

After Treatment

% Change/Year

Average

Change

Control 2009

5.4 squirrels

3.6 squirrels

33%

32.5%

Control 2010

6.3 squirrels

4.3 squirrels

32%

Bait Only 2009

8.3 squirrels

3.4 squirrels

59%

55.5%

Bait Only 2010

6.3 squirrels

3.3 squirrels

52%

Bait & Prebait 2009

10.7 squirrels

2.7 squirrels

75%

71%

Bait & Prebait 2010

6.9 squirrels

2.3 squirrels

66%

Conclusions

In both 2009 & 2010 fewer ground squirrels were observed on the treatment sites than the untreated sites. The treatment sites that were pre-baited exhibited the greatest reduction in ground squirrel numbers after baiting. These observations support the premise that the use of pre-baiting as part of an integrated ground squirrel damage control program using zinc phosphide resulted in a greater reduction of the population than baiting alone.

This education program has helped many farmers save money by reducing the number of squirrels that are eating their crops. In this project we have strived to educate all the farmers in the area on the importance of controlling the ground squirrel and have given them a program to help them accomplish this. The majority of the affected farmers are implementing a control program. In order to significantly reduce the number of squirrels in the entire affected area we will need all the farmers to make this a priority.